Early trigeminal evoked potentials in tumours of the base of the skull and trigeminal neuralgia

Early scalp responses evoked by stimulation of the infraorbital nerve (W1, W2, W3) have been investigated in 23 patients affected by tumours of the base of the skull (parasellar area and cerebello-pontine angle) and in 38 patients suffering from ‘idiopathic’ trigeminal neuralgia. Differences in conduction times between healthy and affected side were evaluated and confronted with data obtained from 30 normal volunteers.Alterations of the response were found in all the patients with tumours of the base of the skull who had clinical signs in the trigeminal area and in 7 of the 12 cases without such signs. The usual pattern of alteration in cases with tumours of the parasellar area was a parallel involvement of W2 and W3 (both absent or delayed to the same extent), whereas in tumours of the cerebello-pontine angle W3 was more seriously affected than W2. Wave W1 was never altered. Pre- and post-operative recording sessions in 2 patients showed definite improvement of the responses after removal of the tumour.In 9 patients suffering from ‘idiopathic’ trigeminal neuralgia delays of conduction were found on the painful side, suggesting that damage to the trigeminal root, possibly at its entry zone into the pons, had taken place. Retrogasserian injection of glycerol was performed in 12 of the 38 patients with trigeminal neuralgia. Stimulation of the operated side showed disappearance of W2 and W3 in 9 cases, prolonged W1–W3 interval in 2 cases and no alterations in 1 case. The extent of response alteration usually paralleled the clinical results.     

Application of stereotactic principles to the treatment of trigeminal neuralgia.

The application of neuroanatomical and neurophysiological principles to the functional surgery of the trigeminal nerve is discussed. Particular attention has been directed toward correlating the three-dimensional anatomical features of the trigeminal nerve and the surrounding structures to the two-dimensional radiograph of this same region. In this regard, 20 trigeminal nerves, including the surrounding neurovascular structures from 10 cadaver sphenoid blocks, were examined. Measurements of the third, fourth and sixth cranial nerves in relation to the profile of the clivus were made from lateral radiographs of the sphenoid blocks. The position of the internal carotid artery in relation to these structures was also noted. These neurovascular relationships are of clinical importance when using the percutaneous thermocoagulation technique for the treatment of trigeminal neuralgia.     

Clinical review of nucleus caudalis dorsal root entry zone lesions for facial pain

Twenty-seven patients with intractable facial pain underwent dorsal root entry zone thermocoagulation lesion of the nucleus caudalis of the spinal trigeminal nucleus. Retrospective review revealed a success rate of 85% in the immediate postoperative period declining to 52% on subsequent follow-up. The best results were in the subgroup of patients with postherpetic neuralgia, of which 67% achieved definite relief. There tended to be some correlation of satisfactory results and pain quality as well as extent of pain along trigeminal territory. The operative morbidity was low although most patients were observed to have a mild transient ipsilateral dysmetria.     

Long-range afferents in the rat spinal cord. II. Arborizations that penetrate grey matter.

1. The caudal extent of the collateral arborizations of entering sensory fibres in rat spinal cord was investigated by two methods: bulk labelling of peripheral nerves by injection of horseradish peroxidase conjugated to cholera toxin (B-HRP) and by antidromic stimulation using small currents from microelectrodes in the spinal cord while recording from single units in peripheral nerve or dorsal root. 2. The results show that injection of B-HRP into the sural or sciatic nerve labelled sural afferents in the grey matter three to four segments caudal to their root entry and sciatic nerve fibres were located in S4, the most caudal segment examined, four to six segments caudal to their root entry. 3. Detailed mapping with microelectrode stimulation showed that the parent descending fibres from filaments dissected from the L1 dorsal root coursed more than 20 mm, seven to eight segments caudal to the entry point in the dorsal columns and sent branches into the grey matter. Single units from the sural nerve were also followed caudally into the S2 and S3 spinal cord segments and also issued collateral branches into the grey matter. 4. The present results suggest that there is close agreement in the caudal penetration of long-ranging afferents by using complementary anatomical and electrophysiological methods.     

Normative data on scalp responses evoked by infraorbital nerve stimulation

Normative data concerning the waves W1, W2, W3, P4, N5, P6 and N7 recorded from the scalp after stimulation of the infraorbital nerve have been collected from 96 healthy subjects, selected according to age and sex. Peak latency, inter-peak intervals, side-to-side asymmetry of inter-peak intervals, amplitude, amplitude ratio of some components versus W1 and side-to-side asymmetry of such ratio have been analysed as functions of age and sex. None of these parameters appeared to be affected by sex; computation of the correlation coefficient showed a significant (P < 0.01), though slight, increase of value of the inter-peak intervals W1–W2 and W1–W3 with age. This increase was partially confirmed by analysis of variance. However, such differences are too small to be useful for practical applications, so only a single normative value is proposed for each parameter. The influence of stimulus strength on the amplitude of the W1 component has been studied in 10 more subjects; amplitude saturation of this wave has been found to take place at intensities between 4 and 6 times the sensory threshold. Increasing the stimulus rate from 1 to 3 pulses/sec did not affect any of the components. It is remarked that components W1, W2, W3 and, to a lesser extent, P4 are the ones to be considered useful in clinical practice.     

Early scalp responses evoked by stimulation of the supraorbital nerve in man

In 25 healthy volunteers the supraorbital nerve was stimulated and evoked potentials were recorded. Leads were placed on the scalp and along the ipsilateral eyebrow-mastoid line and were either referred to a non-cephalic reference (on the neck, or Cv7) or linked to form bipolar derivations. As template wave form was chosen the one obtained from derivation Cz-Cv7, which had an initial triphasic component with negative (SW1a), positive (SW1b), negative (SW1c) polarity (mean latencies 0.63, 0.95 and 1.43 msec), followed by 2 negative waves (SW2 and SW3, mean latencies of 2.20 and 2.89 msec). A final positive wave could be observed in most cases (SP4, mean latency of 4.08 msec). The records collected from the various derivations showed that each component (SW1, SW2, SW3 and SP4) had a different behaviour, thus suggesting separate origins. SW1 would originate from a volley travelling from the point of stimulation towards the mastoid, probably across the ophthalmic branch of the trigeminal nerve. The subsequent components would be generated by deeply situated structures: double pulse stimulation suggests that SW1, SW2 and SW3 are generated before the first synapse, whereas SP4 is a postsynaptic event. A strong similarity exists between the components evoked by stimulation of the supraorbital and the infraorbital nerves. Local anaesthetic block of the frontal nerve on the stimulated side and monitoring of the EMG activity of m. orbicularis oculi and m. frontalis ruled out any muscle contamination of the responses described in this paper.     

Contributions from the auditory nerve to the brain-stem auditory evoked potentials (BAEPs): results of intracranial recording in man

Intraoperative recordings obtained from electrodes placed on the scalp (vertex and earlobe or ear canal) in response to click stimulation were compared with recordings made directly from the auditory nerve in patients undergoing microvascular decompression (MVD) operations to relieve hemifacial spasm (HFS) and disabling positional vertigo (DPV). The results support earlier findings that show that the auditory nerve is the generator of both peak I and peak II in man, and that it is the intracranial portion of the auditory nerve that generates peak II. The results indicate that the second negative peak in the potentials recorded from the earlobe is generated by the auditory nerve where it passes through the porus acusticus into the skull cavity, and that the proximal portion of the intracranial portion of the auditory nerve generates a positive peak in the potentials that are recorded from the vertex. This peak appears with a latency that is slightly longer than that of the second negative peak in the potentials recorded from the earlobe (or ear canal). The second negative peak in the recording from the ear canal and the positive peak in the vertex recording contribute to peak II in the differentially recorded BAEP. Since our results indicate that the difference in the latency of the second negative peak in the recording from the earlobe and that of the positive peak in the vertex recording represents the neural travel time in the intracranial portion of the auditory nerve, this measure may be valuable in the differential diagnosis of eighth nerve disorders such as vascular compression syndrome.     

Spine and scalp somatosensory evoked potentials in normal subjects and patients with spinal cord disease: Evaluation of afferent transmission

Spine and scalp somatosensory evoked potentials (SEPs) to peroneal nerve stimulation were recorded from 20 normal subjects using 1 restricted and 3 open frequency filter bandpasses. Spine to spine and spine to scalp propagation velocities were calculated. Of those recording parameters investigated, optimal recordings were obtained using an open bandpass (5–1500 or 30–1500 Hz) and recording from 3 surface spine bipolar channels and 1 scalp bipolar channel. This method was then investigated in 40 patients with disease of the spinal cord and peripheral nervous system. Focal spinal cord compressive lesions generally resulted in slowing of spine to spine and spine to scalp propagation velocities. Diffuse or multifocal lesions of the spinal cord generally resulted in the absence of scalp responses. Although there was no consistent correlation of the SEP findings with the sensory exam, there was a correlation of the SEP findings with the clinical prognosis.     

On the nature of the afferent fibers of oculomotor nerve

The oculogyric nerves contain afferent fibers originating from the ophthalmic territory, the somata of which are located in the ipsilateral semilunar ganglion. These primary sensory neurons project to the Subnucleus Gelatinosus of the Nucleus Caudalis Trigemini, where they make presynaptic contact with the central endings of the primary trigeminal afferents running in the fifth cranial nerve. After complete section of the trigeminal root, the antidromic volleys elicited in the trunk of the third cranial nerve by stimulating SG of NCT consisted of two waves belonging to the A delta and C groups. The area of both components of the antidromic volleys decreased both after bradykinin and hystamine injection into the corresponding cutaneous region and after thermic stimulation of the ipsilateral trigeminal ophthalmic territory. The reduction of such potentials can be explained in terms of collision between the antidromic volleys and those elicited orthodromically by chemical and thermic stimulation. Also, capsaicin applied on the nerve induced an immediate increase, followed by a long lasting decrease, of orthodromic evoked response area. These findings bring further support to the nociceptive nature of the afferent fibers running into the oculomotor nerve.     

Intracranial recording of short latency somatosensory evoked potentials in man: Identification of origin of each component

In normal subjects the short latency SEPs generally consisted of 3 positive waves (P9, P11, P14) and a succeeding negative wave (N20). To determine the origins of these waves we have made intracranial records from 17 patients, which suggest the following results. P9 originates in stimulated median nerve peripheral to the dorsal roots such as brachial plexus, P11 in the dorsal column of the cervical cord, P14 in the cuneate nucleus and medial lemniscal pathway, and N20 in the cerebral cortex. On the basis of intracranial and intraspinal records, the onset of P11 indicates the arrival of the afferent volley at the cord entry and the peak latency of P11 its arrival time at the C1–2 level dorsal column. The onset latency of P14 indicates the onset of postsynaptic events in cuneate nucleus neurons and the peak latency of P14 arrival at the midbrain.From the ventral surface of the brain-stem 3 positive waves (P′9, P′11, P′14) like the initial positive components of the scalp short latency SEPs (P9, P11, P14) were recorded. The amplitude of P′14 was large compared to that of P14. The peak latencies of P′14 recorded at the medulla and the pons were shorter than that of P14 by 0.7–0.8 msec and 0.2–0.5 msec, respectively. The peak latency of P′14 at the midbrain was almost the same as that of P14. By measuring the distance between the recording electrodes in the brain-stem and the peak latency difference of P′14, the fastest lemniscal conduction velocity was estimated as 56 m/sec.     

Epileptiform activity in the somatosensory cortex of rats with trigeminal neuralgia]

It was shown in experiments on rats that penicillin 1 microliter microinjection (100 U) into the caudal nucleus of the spinal tract of the trigeminal nerve, accounting for formation of a generator of pathologically enhanced excitation (GREE), brings about in rats the pain syndrome with characteristic for trigeminal neuralgia behavioural manifestations and the emergence of epileptiform activity in the somatosensory cortex, especially pronounced in the contralateral hemisphere. The emergence of this activity reflects, on the one hand, the action of the GREE in the caudal nucleus of the trigeminal nerve and, on the other hand, the involvement of the somatosensory cortex taking over stimulation from the hyperactive caudal nucleus, into formation of a pathological algic system of this form of trigeminal neuralgia.     

The magnetite-based receptors in the beak of birds and their role in avian navigation

Iron-rich structures have been described in the beak of homing pigeons, chickens and several species of migratory birds and interpreted as magnetoreceptors. Here, we will briefly review findings associated with these receptors that throw light on their nature, their function and their role in avian navigation. Electrophysiological recordings from the ophthalmic nerve, behavioral studies and a ZENK-study indicate that the trigeminal system, the nerves innervating the beak, mediate information on magnetic changes, with the electrophysiological study suggesting that these are changes in intensity. Behavioral studies support the involvement of magnetite and the trigeminal system in magnetoreception, but clearly show that the inclination compass normally used by birds represents a separate system. However, if this compass is disrupted by certain light conditions, migrating birds show ‘fixed direction’ responses to the magnetic field, which originate in the receptors in the beak. Together, these findings point out that there are magnetite-based magnetoreceptors located in the upper beak close to the skin. Their natural function appears to be recording magnetic intensity and thus providing one component of the multi-factorial ‘navigational map’ of birds.     

Evaluation of reference sites for scalp potentials evoked by painful and non-painful sural nerve stimulation

The objective of this study was to evaluate reference sites for recording the middle- and long-latency scalp potentials elicited by painful and non-painful sural nerve stimulation. Somatosensory evoked potentials (SEPs) were recorded from the scalp, the mastoid, the earlobe, the neck, and the wrist. Each site was referenced to the sterno-vertebral (SV) electrode, which is a balanced non-cephalic reference with essentially no ECG contamination.There was little or no activity recorded between the wrist and SV, and the SV was located within a region extending from the rostral neck to the wrist where the potentials were stable over space. Hence, the SV reference is indifferent for the middle- and long-latency potentials evoked by painful and non-painful sural nerve stimulation. There was, however, significant activity recorded from the earlobe and mastoid, sites which are frequently used as references for the SEP. It is important that investigators using these cephalic references to study the middle- and long-latency peaks of the SEP be aware of this activity as it will distort SEPs recorded from single sites and the SEP scalp topography, distortions which could unnecessarily complicate their interpretation.     

CT引导下立体定向射频热凝三叉神经半月节对原发性三叉神经痛的疗效分析

目的：分析CT引导下立体定向射频热凝三叉神经半月节对原发性三叉神经痛的疗效,探讨其临床适用性。方法：选择从2011年5月至2012年12月于我院住院治疗原发性三叉神经痛的58例患者,在三维CT引导下采用通过BrainLAB手术计划系统经前入路卵圆孔穿刺三叉神经半月神经节,术中根据疼痛分布范围射频热凝三叉神经半月节。观察并比较治疗前后的VAS评分,临床疗效,术中和术后不良反应情况。结果：58例患者的穿刺手术均成功,术后1d、3d、6d的VAS评分均较治疗前显著降低（P〈0．01）;1周后58例患者中,有53例患者疼痛完全消失,l例患者偶然出现疼痛,但无需服用药物处理,共显效54例;4例患者疼痛有所减轻或疼痛发作频率降低,但仍需服用药物,或服用药物剂量较治疗前明显减少;疼痛无改善或者非用药不能缓解的持续痛仅1例。总有效例数为57例,总有效率达98．26％。术中发生不良反应6例,在术后均有所缓解。术后发生各种并发症共15例,均未明显影响手术效果。结论：CT引导可以较为准确的进入穿刺部位,使立体定向射频热凝三叉神经半月节手术更加顺利,达到治疗原发性三叉神经痛的理想效果,适合临床长期推广应用。     

Effects of high potassium solutions and caffeine on the processes of exo-endocytosis of synaptic vesicles at the frog motor nerve ending

In experiments on the frog motor nerve endings of cutaneous pectoris muscle using fluorescent microscopy it has been shown that initiation of massive transmitter release of synaptic vesicles by high potassium solutions in using endocytotic marker FM 1-43 at the nerve terminals light spots occurred only at some of the nerve terminals or at the some parts of nerve terminal. It has been revealed that application of caffeine increased the number of light terminals. Using extracellular microelectrode recording, we showed that both high potassium solutions and caffeine increased frequency of miniature end-plate potentials in a dose-dependent manner. However, high potassium solutions always increased the frequency of spontaneous transmitter release while caffeine increased it only in some experiments. It was concluded that processes of exo- and endocytosis can be caused both by entry of Ca ions at the nerve ending during depolarization (high potassium solutions) and by Ca release from endoplasmic reticulum (caffeine). Possible spatial localization of endoplasmic reticulum at the motor nerve ending is discussed. The hypothesis of its role at the remodeling of synapse was proposed.     

Intracranial recording from the brain-stem and the trigeminal nerve following upper lip stimulation

Short latency evoked potentials following stimulation of the upper lip were recorded intracranially during neurosurgical procedures in 14 patients. In 10 patients, a suboccipital craniectomy provided direct access to the trigeminal root and the pons at the root entry zone. Direct recordings from the trigeminal root were characterized by a large triphasic potential at 2.4–2.7 msec. The latency of this potential increased as a result of moving the recording electrode proximally towards the brain-stem. The same potential could be recorded from the brain-stem surface at a latency suggesting an intra-axial presynaptic origin. A second component, N4.7, was recorded from over the most rostral aspect of the brain-stem in 3 patients and from the tentorium free edge in 4 patients. This potential of smaller amplitude did not show significant difference in latency or polarity at various electrode locations, suggesting a deep diencephalic origin remote from the recording electrode.     

Origin and distribution of P13 and P14 far-field potentials after median nerve stimulation. Scalp,nasopharyngeal and neck recording in healthy subjects and in patients with cervical and cervico-medullary lesions

We studied median nerve SEPs in 10 healthy subjects, by means of simultaneous recording over the scalp, around the neck and near the ventral surface of the medulla using a nasopharyngeal (NP) electrode. This recording technique enabled us to clearly differentiate P13 and P14 potentials. The former was always found in NP records, while the latter was more evident in scalp traces. The same technique was used to study 9 patients with various lesions of the cervical cord or cervico-medullary junction. Patients with high cervical lesions demonstrated abnormalities of both P13 and P14 potentials, while patients with lesions of the cervico-medullary junction demonstrated a clear dissociation between normal P13 in scalp and NP traces, and abnormal scalp P14. Patients with lower cervical lesions, selectively involving the central grey matter, showed normal P13 and P14 potentials, in spite of abnormal N13 cervical responses. Our findings strongly suggest that both scalp and NP P13 have the same generators in higher segments of the cervical cord, and that NP more than scalp records are effective in analyzing the P13 response. We suggest that the selective recording of the P13 potential could be useful in the assessment of focal lesions of the higher cervical cord or of the cervico-medullary junction.     

Radiofrequency thermocoagulation of Gasserian ganglion and its rootlets for trigeminal neuralgia.

Thirty-nine patients with trigeminal neuralgia, not controlled by medical treatment, were treated by radio-frequency thermocoagulation of the Gasserian ganglion and its posterior rootlets. Thirty-six received satisfactory pain relief. In 30 patients touch sensation in the treated territory was preserved. The corneal reflex was affected in only six patients, two of whom subsequently developed keratitis. There were no other complications apart from a minor unpleasant sensation in eight patients. By selectively destroying pain fibres this technique offers the scope of preserving touch sensation in the treated area. Moreover, the zone of analgesia can be restricted to the affected region by sensory mapping through electrode stimulation before thermocoagulation. Its simplicity, low morbidity, associated short hospital stay, and the increased ability to preserve touch sensation, especially of the cornea, seem to make it preferable to other forms of surgical management for trigeminal neuralgia.     

Results of treatment of trigeminal neuralgia by microvascular decompression of the Vth nerve at its root entry zone.

Eighty five patients suffering from trigeminal neuralgia resistant to medical therapy underwent surgical treatment for relief of pain at the Department of Neurosurgery University Alexander Hospital Sofia from 1981 until 1997. Microvascular decompression at the root entry zone of the V(th) nerve has been performed using the technique of Jannetta. The operative exploration of the parapontine root entry zone disclosed neurovascular conflicts in 87.1% of the cases. They represented displacement and/or distortion, sometimes pressure grooves, discoloration, altered vascularity of the V(th) nerve. The analysis of early postoperative results have shown an excellent outcome in 90.6% of the cases, good in 3.5% and poor in 2.4% with mortality of 3.5% early in these series when no postoperative monitoring was available. The follow up study one year after surgery revealed 90.2% excellent and 3.7% good results and poor outcome and recurrences in 6.1% of the cases. Patients with long lasting trigeminal neuralgia, previous destructive procedures, venous compression, lack of convincible evidences for neurovascular conflicts had less favorable outcome or recurrences. In the last years partial sensory rhizotomy was performed in cases when no neurovascular conflicts were found out. Patients with unquestionable arterial compression leading to displacement associated with distortion and pressure grooves had excellent outcomes. Early recurrences were associated with missed pathology at the entry zones. During reexplorations for late recurrences new arterial compression was found in less than half of the cases.     

小鼠眼神经注入Dil后三叉神经节的形态学研究

目的：经眼神经注入DiI研究小鼠三叉神经节的形态学结构。方法：小鼠10只,体重25—30克,雌雄不拘,进行灌注固定后,在外科显微镜下开颅并确认三叉神经节和眼神经,分别于双侧眼神经植入DiI染色晶体。37℃恒温箱放置3个月,待DiI染色晶体扩散后,取出植入DiI染色晶体的眼神经和三叉神经节,再根据神经走向切片,通过荧光显微镜观察DiI染色晶体在三又神经节内的分布。结果：眼神经离三叉神经节约1cm处植入DiI染色晶体后,应用荧光显微镜明视野观察,均可见到高密度标记的眼神经纤维,行向后内,穿经眶上裂入颅。逐步靠近三叉神经节外上方,并进入三叉神经节内,眼神经标记的神经元位于三叉神经节的前内侧。在三叉神经节内可见到DiI标记的神经节细胞及神经纤维。神经纤维平行致密排列,并被神经节细胞神经纤维分隔成群或簇。神经节细胞呈圆形和卵圆形,大小不一,部分节细胞呈蜂窝状排列。亦可见神经元的突起,有的呈螺旋状连于胞体,有的呈线状连于胞体,并可见到双极神经元。结论：小鼠经眼神经注入DiI后,三叉神经节细胞和神经纤维的排列循序跟其他动物基本一致。